The present invention relates to the ion exchange resin beads which are for example useful for reducing the concentration of multi-valent alkaline earth or transition metal cations in an aqueous solution, to processes for preparing these ion exchange resin beads and to the use of the ion exchange resin beads.
It is well known in several areas of technology that cations of the alkaline earth metals and transition metals are desired to be removed from solutions due to their value or to the detrimental effects they can cause. For example, there are situations where these cations are desired to be removed from the solutions, to the greatest extent possible, prior to the
a) use of the liquid in chemical or separation processes, PA1 b) consumption of the liquid or PA1 c) release of the liquid into the environment. PA1 i) (aminomethyl)(hydroxymethyl)phosphinic acid groups and PA1 ii) a matrix of a cross-linked polymer wherein the level of cross-linkages is decreased in the shell area as compared to the core area. PA1 i) primary or secondary amino groups and PA1 ii) a matrix of a cross-linked polymer wherein the level of cross-linkages is decreased in the shell area as compared to the core area with PA1 q is zero; PA1 each R.sup.3 independently is hydrogen or a cation; PA1 each R.sup.4 independently is hydrogen, alkyl, cycloalkyl or aryl; and PA1 m is from 1 to 12, preferably from 1 to 6, more preferably from 1 to 3, PA1 by reacting resin beads having groups of formula ##STR2## wherein X is halogen and R.sup.4 and m have the meanings stated above and having an above mentioned matrix
It has long been known that it is possible to exchange detrimental ions in a stream with more acceptable ions and/or chelate ions to remove them from the streams. In this regard there have been many developments made over the years in this area of specialized polymeric resins and specialized functional groups which can be chemically bound to such resins to provide improved systems for the removal of various anions and cations. Notwithstanding this activity it remains quite unpredictable which combinations of functional groups and polymeric resins will prove to be suitable for the removal of a particular type of ion. The published PCT application WO 83/02947 discloses macroporous alkylaminophosphonic chelating resins for purifying brines. British Patent 853,834 relates to ion-exchange resins containing substituted-aminomethyl phosphonate groups.
British Patent Specification 1,230,363 discloses shaped shell graft copolymeric particles which comprise an inert polymeric nucleus having grafted on it a polymeric shell. The nucleus may be cross-linked. The shell contains separate and discrete regions of ion exchange reactive groups "opposite signs". By "opposite signs" is meant that the shell contains a) anion and cation exchange groups or b) strongly basic and weakly basic groups or c) strongly acidic and weakly acidic groups.
Published German Patent Application 1,695,449 discloses a process for preparing substituted (aminomethyl)phosphinic acids by reacting hypophosphorous acid with an amine and an aldehyde. If the produced (aminomethyl) phosphinic acids are polymeric compounds, they can be used for impregnating materials as for ion exchange applications.
In the published German Patent Application 28 48 289 and British Patent Application 2 040 950 macroporous styrene-divinylbenzene polymers containing (aminomethyl)(hydroxymethyl)phosphinic acid groups have been suggested for selectively separating the cations and anions of heavy metals such as WO.sub.3.sup.2- and Cu.sup.2+. Such functionalized polymers are prepared according to the teaching of German Patent Application 38 48 289 by aminating cross-linked chloromethylated styrene-divinylbenzene polymers with urotropin (hexamethylene tetramine), monoethanolamine, or ethylene diamine and reacting the aminated polymer with formalin (an aqueous solution of formaldehyde), sodium hypophosophite and concentrated hydrochloric acid. However, the optimized macroporous styrene-divinylbenzene polymers containing (aminomethyl)(hydroxymethyl)phosphinic acid groups do not have an excellent copper capacity. In particular when these macroporous polymers containing alpha-aminophosphinic acid groups are used in aqueous solutions are an elevated temperature, their copper or calcium capacity is insufficient for some applications.
Accordingly, it would be desirable to provide new polymers containing ion exchange groups which have the same or a higher cation exchange capacity such as copper capacity or calcium capacity. Since many processes for removal of certain cations from solutions are advantageously carried out at elevated temperatures, typically from about 35.degree. C. to about 70.degree. C., such as the removal of calcium from brine solutions used for the production of chlorine, it would be particularly desirable to provide new polymers containing ion exchange groups which have a high cation exchange capacity, such as calcium or copper capacity, at elevated temperatures. By "elevated temperatures" is meant 35.degree. C. or higher, preferably at least about 40.degree. C.
In many ion exchange processes, the resins are subjected to stresses which cause substantial breakage in the beads. Said stresses may be mechanical, i.e., due to crushing or collisions between beads or the beads and their containers, or osmotic, such as when the beads are subjected to sudden or repeated changes in electrolyte concentration. The breakage of the ion exchange beads causes substantial losses in the efficiency of the ion exchange column and large costs in replacing the broken resins.
Accordingly, it would also be desirable to provide new polymers containing ion exchange groups which have a high resistance to osmotic shock or to mechanical stress.
Furthermore, it would be desirable to provide a new, efficient process for preparing these polymers.